“ LEAF SURFACE temperature is almost always different than ambient air temperature .”
feature leaf surface temperature
“ LEAF SURFACE temperature is almost always different than ambient air temperature .”
WHAT AFFECTS LEAF SURFACE TEMPERATURE ?
Ambient air temperature , relative humidity , leaf physiology and pigmentation , genetic / metabolic differences , and light spectrum all affect LST . Air temperature sets a baseline for leaf temperature , providing warmth to leaves cooler than the air , and cooling leaves warmer than it . Many leaves can cool themselves through evaporation of water through stomata ; higher relative humidity typically increases leaf surface temperature by reducing this evaporative cooling . The spectrum ( colours ) of light the leaf is receiving also affect leaf surface temperature .
Many studies have shown that chlorophyll , the primary driver of photosynthesis , most efficiently uses light in the blue and red areas of the light spectrum . This does not mean that plants cannot use green or yellow light for photosynthesis , just that it is less efficiently used . We can slightly modify the popular game of Bags and use it as an analogy to understand how photons can fuel photosynthesis . Imagine a Bags board representing the leaf , but instead of one hole near the center , there is one near the top and one near the bottom . The top hole represents the higher energy blue photons and the bottom hole the lower energy red photons that chlorophyll can utilize . Each bag thrown at the board represents a photon of light . If you throw a bag through the blue hole it efficiently fuels photosynthesis . Same for a red photon — it will go into the red hole and fuel photosynthesis .
If a photon of a different colour such as yellow or green hits the board , it will slide down the board , creating heat from friction and changing colour as it slides down and loses energy . It may slide down and fall through the red hole , which will fuel photosynthesis , or the photon could slide off the bottom of the board , not fueling photosynthesis and only creating heat . This analogy demonstrates that optimizing the spectrum of light ( targeting bags at holes , not just the board ) can increase photosynthesis while also keeping the leaves cooler ( less bags sliding down the board ). Therefore , measuring leaf surface temperature indirectly measures the efficiency of the light spectrum mix for growing plants — a less-efficient spectrum will tend to heat the leaf more , while a more-efficient spectrum mix will heat the leaf less , as more of the original light energy is being converted directly to chemical energy instead of heat . Light spectrums optimized for plants will therefore require a warmer ambient air temperature to keep the LST in the ideal range than spectrums not optimized for plants . Since heat mitigation is generally a concern in indoor gardens with artificial light , these higher ambient temperatures can save significant money .
ARTIFICIAL GROW LIGHTS
Various artificial grow light technologies create different light spectrums . LED grow lights differ significantly from other forms of artificial plant lights in that the spectrum can be tailored to any specification , eliminating unwanted excesses of light wavelengths ( colours ) while providing light plants can use most efficiently . Other artificial lighting technologies produce much of their light as an unintended and unavoidable byproduct of how they operate , ultimately wasting energy in heating up plant leaves . Of course , an LED light with a spectrum not optimized for plants will also waste energy heating up plant leaves . High pressure sodium ( HPS ), in particular , converts a significant portion of the energy consumed by the bulb directly to non-visible infrared light in the 810-830-nanometre ( nm ) range , peaking at about 819 nm . This infrared light is perceptible to you ( and plants ) by the warmth it creates , although it does not have enough energy for photosynthesis . Additionally , much of the visible light HPS bulbs produce is yellow , intermediate in energy between blue and red light most efficiently utilized by plants , warming up the leaves .
OBSERVING HOW SPECTRUM AFFECTS LST
There are several tools available for measuring actual leaf surface temperature , from probes placed on the leaf to infrared thermometers . Many of these give an accurate reading of LST at a single point , but looking at only a single point on a leaf provides an incomplete idea of the temperature , since it can vary significantly over the surface of a single leaf . A forward-looking infrared camera ( FLIR ) provides a complete picture of leaves ’ temperature and a much better understanding of how light spectrum affects LST .
50 grow cycle